The present invention relates to a control gauge designed to verify, on exiting a manufacturing line, that the dimensional characteristics of a fastener comply with the fastener's design plan. More specifically, the invention relates to a control ring for a fastener of the type comprising an enlarged head and a cylindrical shaft extending along an axis, the shaft comprising at least one band of coating parallel to or in the direction of the axis. Such a fastener is described in application FR 3 008 754 and represented in FIGS. 1A and 1B, published in US2016/0083109, incorporated herein by reference. This type of fastener is used to assemble metal and composite structures in airplanes.
FIGS. 1A and 1B represent a metal fastener 10 of the aforementioned type, respectively in end and side views, comprising a protruding head 12, a cylindrical shaft 14, and a threaded portion 16. In variants, the fastener can comprise a pulling stem that makes it possible to pull on the fastener to insert it by interference in a previously-drilled structure. This stem may be an integral part of the fastener 10, or removable by means of a threaded extremity inserted into a tapped extremity made inside the threaded portion 16. In variants, the threaded portion can be replaced by annular crimping grooves. In variants, the head 12 can be countersunk.
The shaft 14 is designed to come into tight contact in a hole made in a set of structures comprising one or more metal and/or composite materials, and comprises four conducting portions 20, i.e. which do not comprise any coating or paint to prevent an electrical current from flowing between the conducting portion of the shaft and the wall of the hole. The shaft also comprises four lubrication bands 22, arranged parallel to the axis of revolution A of the fastener. Each lubrication band 22 extends over the shaft 14 and over a portion beneath the head 12, over a distance X. The conducting 20 and lubrication 22 portions are arranged alternately around the circumference of the shaft, as shown in FIG. 1A. In this way, electrical conduction is provided over the entire thickness of the assembled structure, irrespective of the composition of the structure wherein the fastener is inserted. The lubrication portions 22 make it possible to provide lubrication of the shaft 14 over its entire height, such that the fastener can be installed by interference without jamming or breaking.
The lubricant used may be a solid MoS2 type of film, or an organic resin with aluminum pigments, such as the HI-KOTE™ 1 or HI-KOTE™ 1NC coatings, both of which are dielectric, marketed by Hi-Shear Corp. in Torrance, Calif. The lubricant is deposited with a thickness of 5 to 13 μm, for example by pulverization, over an axial length and width specified in the design plan of the fastener 10.
Irrespective of the means of manufacturing of a fastener 10 and of the means of depositing the lubrication bands 22, the dimensional characteristics of these bands—particularly the lengths and widths—must be measured and compared with those of the fastener's design plan to ensure their compliance.
Various dimensional measurement means are known that make it possible to verify the dimensions of the bands 22, which are specified in the fastener's design plan.
A first means is a 3D means, which makes it possible to verify the dimensions by palpation of the fastener. A second known means is a computerized means comprising a camera that films the fasteners and analyzes the images in comparison with a reference image.
These means are reliable, but expensive to buy and maintain, bulky, fragile, and require specially-trained staff.
One objective of the present application is to provide a means for dimensionally verifying the lengths and widths of the lubrication bands of fasteners of the prior art that is easy to manufacture, simple and quick to use, that suffers little from wear and that is reliable.